Conventionally, as organic glass, which is light as compared with inorganic glass, polymers of diethyleneglycol bis(allylcarbonate) such as CR-39 (product name, manufactured by PPG Industries) and polymers of methyl methacrylate are used. The higher the refractive index of the glass is, the further reduced the thickness of the lens can be. The refractive indices of these organic glasses are in a range of 1.49 to 1.50, relatively low as compared with inorganic glasses (in case of white crown glass, the refractive index is 1.523.) Therefore, in a case where lens is prepared from an organic glass, the edge is thick as compared with a case where inorganic glass is used and therefore, advantages of weight reduction are decreased. Moreover, in a case where an organic glass is used for vision correction lens for high degree, there is a disadvantage that the look of the lens is bad. For this reason, resin for optical material giving polymer with high refractive index has been desired.
In terms of method for enhancing refractive index of an organic glass, various attempts have been made so far. For example, in Japanese Patent Application Laid-Open No. S63-46213 (U.S. Pat. No. 4,775,733), as an optical resin which can impart high refractive index, thiourethane-base resin obtained by reacting isocyanate compound with mercapto compound is described. But there are problems with thiourethane-base resin that isocyanate compound serving as raw material is toxic and that thiol compound serving as raw material has an odor.
Further, in Japanese Patent Application Laid-Open No. 3-217412, (meth)acrylate compound containing sulfur atom is described as material giving high refractive index. Although these materials can provide a relatively high refractive index, the refractive index is not necessarily high enough.
Furthermore, in Japanese Patent Application Laid-open No. 2002-275216 (U.S. Pat. No. 6,794,471), a (meth)acrylate compound having dithiolane ring structure which enables high refractive index is proposed. The refractive indices of these compounds are high. However, since their structures include sulfide, good photocuring can be obtained but sulfide tends to be oxidized in molding process through thermal curing with peroxide as initiator and therefore, control of polymerizability is not necessarily satisfactory.
In addition, in Japanese Patent Application Laid-Open No. 2004-323702, copolymer of (meth)acrylate compound having a cyclic dithiocarbonate structure and isobornyl (meth)acrylate compound is disclosed. However, such a copolymer cannot be said to give a sufficiently high refractive index in some technical fields where the compound is used, either.